1. Field of the Invention
The present invention relates to a light source apparatus, and more particularly to a light source apparatus that calculates a junction temperature, and controls electric power that drives a light source.
2. Description of the Related Art
Conventionally, a light source apparatus has been developed which is capable of special light imaging such as narrow band observation (narrow band imaging: NBI) that enables observation of a vicinity of a mucosal epithelium of living tissue, in addition to normal observation (white light imaging: WLI) using white color illumination. In the light source apparatus, a turret including a plurality of optical filters is included, and an optical filter corresponding to an imaging mode is disposed on an optical path of a xenon lamp, whereby switching of a mode of normal observation or special light imaging is realized.
Further, in recent years, with enhancement in the light intensity of a white color LED, light source apparatuses using LEDs have also been developed in an endoscope field. Further, in the endoscope field, needs for narrow band observation are growing, and therefore, a configuration of a light source apparatus that can perform narrow band observation by using a white color LED and a purple LED is contrived.
FIG. 8 is a diagram showing light intensity deterioration characteristics of a white color LED and a purple LED. As shown in FIG. 8, the white color LED and the purple LED have different light intensity deterioration characteristics, and therefore even with the same lighting time periods, the light intensities of the white color LED and the purple LED differ from each other. Therefore, the light source apparatus including LEDs of a plurality of colors needs processing of correcting the light intensity of each of the respective LEDs.
For example, Japanese Patent Application Laid-Open Publication No. 2000-29980 discloses the optical reading apparatus that can extend the product life by automatically compensating deterioration of the LEDs due to secular change, and can keep a sufficient reading ability for a long period of time. The optical reading apparatus executes deterioration compensation processing after 3000 hours and 5000 hours by estimating reduction, namely, deterioration of luminance of the LEDs due to secular change.